1. Field of the Invention
The present invention relates to an image reading apparatus that scans and reads an image of an original and an image forming apparatus provided with the same.
2. Related Art
An image forming apparatus such as a copy machine that forms an image on paper by xerography is provided with an image reading apparatus for optically reading an image of an original. The image reading apparatus is generally provided with an optical system carriage including a light source, a mirror and the like. The image reading apparatus is configured to move the optical system carriage in a sub-scanning direction in a housing, which is a box-shaped structure, so as to read the image of the original by an image sensor such as CCD converting the image into an electric signal.
A driving unit that moves the optical system carriage includes one employing a belt drive system. Such a driving unit is configured to include a belt that moves the optical system carriage in the sub-scanning direction, a pair of pulleys between which the belt is stretched, a pin that rotatably supports a first pulley, which is a driving pulley, of the pair of pulleys, and a driving motor that rotationally drives the driving pulley.
Here, a stepping motor that can provide positioning by open loop control is often used as the driving motor. A driving device is proposed that is configured to prevent vibration of such a stepping motor from being transmitted, which decreases image quality, by forming a timing belt with a material of high elasticity and attaching the stepping motor to a frame via an antivibration member.
In the above prior art configuration, pins that support pulleys may fall due to tension of the timing belt and cause disalignment of pulleys. In addition, as the stepping motor is attached to the frame via the antivibration member made of an elastic body, alignment of the pulleys may be deteriorated by elastic deformation of the antivibration member. Such deterioration of alignment applies lateral pressure to the timing belt, thereby causing color shift in a color image forming apparatus.